Caspase-1 (interleukin-1β-converting enzyme) is inhibited by the human serpin analogue proteinase inhibitor 9

Abstract

The regulation of caspases, cysteine proteinases that cleave their substrates after aspartic residues, is poorly understood, even though they are involved in tightly regulated cellular processes. The recently discovered serpin analogue proteinase inhibitor 9 (PI9) is unique among human serpin analogues in that it has an acidic residue in the putative specificity-determining position of the reactive-site loop. We measured the ability of PI9 to inhibit the amidolytic activity of several caspases. The hydrolysis of peptide substrates by caspase-1 (interleukin-1beta-converting enzyme), caspase-4 and caspase-8 is inhibited by PI9 in a time-dependent manner. The rate of reaction of caspase-1 with PI9, as well as the rate of substrate hydrolysis of the initial caspase-PI9 complex, shows a hyperbolic dependence on the concentration of PI9, indicative of a two-step kinetic mechanism for inhibition with an apparent second-order rate constant of 7x10(2) M(-1).s(-1). The hydrolysis of a tetrapeptide substrate by caspase-3 is not inhibited by PI9. The complexes of caspase-1 and caspase-4 with PI9 can be immunoprecipitated but no complex with caspase-3 can be detected. No complex can be immunoprecipitated if the active site of the caspase is blocked with a covalent inhibitor. These results show that PI9 is an inhibitor of caspase-1 and to a smaller extent caspase-4 and caspase-8, but not of the more distantly related caspase-3. PI9 is the first example of a human serpin analogue that inhibits members of this class of cysteine proteinases.

Serine Protease Inhibitor 6 Plays a Critical Role in Protecting Murine Granzyme B–Producing Regulatory T Cells

“…In keeping with both our in vitro data and in vivo GVHD data, GrB-expressing Tregs in the heart and draining LNs displayed higher rates of apoptosis in the absence of Spi6. It is important to note that the Proteinase inhibitor 9 (PI9) human homologue of Spi6 was suggested to be an inhibitor of caspase 1 that regulates key steps in inflammation (29, 30). Therefore there is a possibility that some of the effects observed in our in vivo mouse models could be related to a defect in IL-1beta production.…”

Serine Protease Inhibitor 6 Is Required To Protect Dendritic Cells from the Kiss of Death

“…Spi6 and the human homologue Proteinase Inhibitor 9 (PI9) (30, 31) also inhibit other proteases. For example Spi6 can inhibit neutrophil elastase (NE) (20) and PI9 inhibits caspase 1(32). However, the complete rescue of DC survival and expansion of anti-LCMV CTL by GrB deficiency argues that at least in this context GrB is the physiological target of Spi6.…”

Serpins in arthropod biology

“…Cysteine proteinase inhibitory serpins include human squamous cell carcinoma antigen 1 (SCCA1) which inhibits cathepsins K, L, and S [151,152], as well as the viral serpin crmA and human P19, which inhibit certain caspases [153,154]. B. mori Serpin18 specifically inhibits cysteine proteinases, including a B. mori fibrinase involved in silk production during development [126].…”